In an effort to prevent leakage of hazardous fluids from piping systems, the use of sealless pumps has become more common. While pumps of this type may employ seals at non-critical locations, the pump's primary characteristic is that a shaft seal is not required. The pump's impeller is caused to rotate by an apparatus that does not penetrate the piping system. In this manner, a primary site for leakage is avoided.
A typical sealless pump makes use of a magnetic coupling to drive the impeller. An example of this type of pump is provided by Zozulin in U.S. Pat. No. 2,827,856. Disclosed in the patent is an axial flow pump in which a cylindrical impeller has exterior magnets that are magnetically coupled to complementary magnets located outside of the pump casing. The exterior magnets are secured to a housing that rotates about the pump casing through the use of a pulley and belt system coupled to a motor. It should be noted that in the Zozulin reference, bushings having end-located seals are positioned at each end of the impeller to support the impeller and to seal its outer surface from the fluid being pumped.
Prior art sealless pumps, while avoiding the shaft seal problems experienced by more conventional pumps, still suffer a number of problems. The pumps typically employ a complicated structure of bearings and/or bushings and/or seals to support the impeller. In addition, various seals are employed to either seal the impeller's outer surface from the fluid being pumped or to route the pumped fluid about the impeller for cooling purposes. This makes the units expensive to manufacture and difficult to maintain. The complexity of the prior art units also adversely affects their durability and expected life-span.